|Publication number||US7397547 B2|
|Application number||US 11/490,575|
|Publication date||Jul 8, 2008|
|Filing date||Jul 21, 2006|
|Priority date||Sep 26, 2005|
|Also published as||US7268864, US7319523, US7471379, US20070070330, US20070070331, US20070070332, US20080001105|
|Publication number||11490575, 490575, US 7397547 B2, US 7397547B2, US-B2-7397547, US7397547 B2, US7397547B2|
|Inventors||Ronald P. Chiarello, Charles Eric Boyd, Duncan A. McPhee|
|Original Assignee||Jetalon Solutions, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (40), Non-Patent Citations (5), Referenced by (6), Classifications (11), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation of U.S. patent application Ser. No. 11/235,622, entitled “Method and Apparatus for a Liquid Chemical Concentration Analysis System,” filed on Sep. 26, 2005, the subject matter of which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to the field of analytical chemical instrumentation utilizing optical sensors and in particular to integrated optical-chemical analytical instrumentation used in the fields of chemical, biochemical, biological or biomedical analysis, process control, pollution detection and control, and other similar areas.
2. Discussion of the Related Art
n1=n2 sin θc (1)
As shown in
The plurality of light rays 59, 60, and 61 strike the sensing surface 64 at a range of angles. For angles of incidence smaller than the critical angle 75, a portion of the light is refracted into the sample 40 resulting in an overall loss. This is illustrated by refractive ray 63 which travels into the sample and reflected ray 65 which reflects into the housing 55 at angle 74.
At the critical angle 75, a light ray 60 reflects along the sensing surface 64 at a 90 degree angle of refraction minimizing the overall light loss into sample 40. Thus, a critical angle 75 can be measured as the angle measured between the incident light ray 67 and the normal to the sensing surface 64. For angles of incidence larger than the critical angle 75, such as 76, the incident ray 69 is totally internally reflected within housing 55, with no refracted component, and its full intensity is therefore directed toward photodetector 90. This total internal reflection can only occur when light originates in a medium of a higher Index of Refraction.
It should be noted, however, that the Index of Refraction of the housing material may be lower than the sample 40. In such a configuration, the sensor 50 can be used to render a threshold level of Index of Refraction eliminating a range less than that of the housing material.
For optical radiation, a suitable photodetector 90 is the TSL213, TSL401, and TSL1401 (manufactured by Texas Instruments Inc. Dallas, Tex.), with a linear array of resolution n×1 consisting of n discrete photo sensing areas, or pixels. Light energy striking a pixel generates electron-hole pairs in the region under the pixel. The field generated by the bias on the pixel causes the electrons to collect in the element while the holes are swept into the substrate. Each sensing area in the photodetector 90 thereby produces a signal on an output with a voltage that is proportional to the intensity of the radiation (60, 65, 70) striking the photodetector 90. This intensity and its corresponding voltage are at their maxima in the total internal reflection region.
Various means of photodetection are contemplated including an n×1 cell photodetector such as the TSL213, TSL401, and TSL1401. In addition, a single cell photo resistor, bolometer, positive sensitive detector, pyrolectric device as well as other devices may be used.
As described, a range of angles of the reflected light rays are projected onto photodetector 90. The critical angle is marked by a transition from high to low intensity. The output, representing bit level data from the photodetector 90, is transmitted within housing 55 via interface 92 to a signal processing unit 95 for further qualitative and/or quantitative analysis.
The signal processing unit 95 may provide the necessary interface control signals, such as clock line and serial input, for protocol communications with the photodetector 90. Signal processing unit 95 may be used increasing the sensor's resolution over that obtained by the photodetector 90 pixel resolution. The use of the signal processing unit 95 is optional.
When used, signal processing unit 95 is preprogrammed to analyze and characterize the intensity, occurrence, and timing of light rays 60, 65, and 70 to obtain qualitative and quantitative information about the sample 40. For example, signal processing unit 95 can be preprogrammed to determine the total amount of time that sample 40 is within a given proximity of the sensor 50. Also, signal processing unit 95 can be preprogrammed to determine the frequency of sample 40 over a given period of time.
Output data from signal processing unit 95 may be transmitted via interface 96 to a secondary system, such as a computer, hand-held meter, calculator, printer, logic analyzer, or other similar system (not shown). The interface 96 comprises a plurality of conductive pins, giving the sensor a platform similar to an integrated circuit package.
Sensor 50 may also include a temperature sensor 98 within the housing 55. Temperature sensor 98 produces an electrical signal indicative of the temperature of the sensor surface 64 during operation thereof. This temperature signal may be relayed to signal processing unit 90 via interface 97. Temperature data can be utilized to compensate for apparent changes in the measured Index of Refraction as a result of changes in the operating temperature.
A filter may be used to screen out radiation at wavelengths other than wavelengths produced by light source 57. This filter (not shown) may overly photodetector 90 and serves to pass radiation at the wavelengths produced by light source 57 to photodetector 90. As such, the filter eliminates unwanted noise caused by other radiation sources in proximity to the sensor 50. One suitable filter is the plastic filter material marketed by Polaroid Corporation and known as XR-84. This material is especially suitable for passing infrared radiation and blocking visible radiation.
An alternative to utilizing a filter is to utilize a plastic or epoxy material for the housing 50 which is transparent to wavelengths produced by the light source 57 and opaque to frequencies outside the desired frequency range of interest for a given sensor/sample combination. Likewise, an absorbing die can be enclosed in the housing to achieve the same function.
The present invention marks a step forward for concentration analysis for liquid chemicals, in that it is a real-time, cost-effective system packaged in a compact form factor that is conveniently integrated into many applications. In the present invention, optical reflectivity (REF) is used to determine the Index of Refraction (IoR) and thereby the chemical concentration of the liquid chemical under analysis.
The present invention consists of a miniaturized fully-integrated optical subsystem, an optical-fluid cell, and an independent electronic circuit. The present invention brings several innovations to concentration analysis made by Index of Refraction.
First, Index of Refraction measurements in themselves do not provide information on chemical concentration. The present invention includes a firmware algorithm (on board an electronic circuit) and a software program for a step-wise calibration method that directly correlates IoR measurements to chemical concentration.
Second, the optical-fluidic cell of the present invention provides for analysis of liquids under both static and dynamic conditions, uses an optically transparent sapphire window that is placed in direct contact with the liquid under analysis and has a refined fluid dynamic design to provide dynamic mixing of solutions and mixtures at the sensing surface. In accordance with the present invention, sapphire provides superior chemical and mechanical integrity and durability over prior art IoR sensors. Dynamic mixing at the sensor surface provides increased resolution and accuracy for concentration analysis. An innovation over the prior art is to place an optical sapphire window in contact with the liquid under analysis. Sapphire has a hardness of 9 (only diamond is harder) and is resistant to chemical attack. This improvement over prior art sensors improves the optical, chemical and mechanical integrity of the sensing surface and provides increased durability, accuracy and resolution.
Third, IoR measurements are highly sensitive to temperature changes of both the liquid under analysis and to electro-optical components. The present invention uses a two-point temperature measurement system and a temperature compensation method via a firmware algorithm on-board the electronic circuit to automatically perform temperature compensation for concentration analysis in real-time. The temperature compensation apparatus and method afford the present invention real-time (˜10 mS) measurement with high resolution (≧0.01% concentration) and high accuracy.
Fourth, another innovation of the present invention is a three stage-signal processing and signal averaging. This innovation also contributes to real-time measurement, high resolution and high accuracy.
Fifth, yet another innovation is a method for automatic compensation of variations in the brightness of the light source as a function of light source temperature. This innovation contributes to real-time measurement, high resolution and high accuracy.
Sixth, another innovation is that the present invention need not determine the critical angle in order to determine IoR and thereby chemical concentration. The present invention uses numerical methods to determine the Mass Moment (MM) of the first numerical derivative of the measured optical reflectivity. The MM value is input into a calibration method that is used to determine IoR and thereby chemical concentration.
In summary, the present invention incorporates several innovations in both apparatus and methodologies to provide significant improvement over prior art IoR sensors.
According to embodiments of the present invention, a chemical concentration analysis sensor and system for liquids are described. In the preferred embodiment, the analysis sensor is used in situ and at the point-of-use. The analysis sensor and system are applicable to many liquid chemical applications. The sensor analyzes concentration for acids, bases, aqueous-based liquids, solvents, slurries, and ultrahigh purity, caustic and corrosive liquids. The invention is useful in manufacturing facilities, water treatment and water recycling/reclaim systems (both industrial and municipal), medical applications, and ground and surface water sources.
In various embodiments, the invention can be integrated into liquid recycling systems, municipal water treatment facilities and into small scale at home water treatment systems. The present invention may be connected to a flowing liquid via input and output lines, immersed into a static reservoir or injected with a sample of a liquid. The analysis system provides concentration information in real-time (0.001-1 seconds), has a compact form factor (<2″×2″×1″) and a concentration sensitivity at or below 0.01%. The analysis system has capabilities as both a monitoring system and as a closed-loop control system for interface with actuators for liquid chemicals such as pumping systems, diverting systems, variable flow valves, waste treatment systems, etc.
In the preferred embodiment of the present invention, the light source 120 is a light emitting diode (LED) and the sensor window 147 is sapphire. The second thermistor 148 may be attached to the front or back of the sapphire window for convenience. The second thermistor 148 may also be placed inside the window 147 or in contact with the liquid under analysis at or near the sensing surface 146.
In the present invention, the optical window 147 is placed in direct contact with the liquid under analysis. The window 147 may be made of any dielectric material, with appropriate optical properties, including sapphire, quartz, borosilicate glass or other suitable materials. In the preferred embodiment of the present invention a window 147 made of sapphire is placed in contact with the liquid under analysis. In the preferred embodiment of the present invention, sapphire is specifically selected as the window 147 material due to its superior properties including; mechanical strength, resistance to chemical attack and scratching, durability, optical quality, strength under pressure, machinability and availability. In accordance with the present invention, the optical window 147 can be adhered via an optical epoxy (or other optically appropriate material) directly to the optical sensor 300 housing or to a glass (or other appropriate material) window 140. Also, in accordance with the present invention, the sapphire window may be coated with a thin layer (˜20-100 Å) of a material of sufficiently low density to allow light from the light source 120 to pass completely through it into the liquid under analysis. In accordance with the present invention, the purpose of the thin coating is to further protect the window surface from damage or deterioration and therefore extend the useful life of the optical sensor 300.
The optical sub-system 510 of the analysis system 500 may include a plurality of optical sensors 300 each having a sensor ID 511 such as a barcode, RF tag or other optical sensor specific identifier to identify a specific optical sensor in question. The sensor ID 511 provides information identifying an optical sensor 300 that is location and/or sample specific depending on the particular sensor application. A sample specific optical sensor 300 can be so labeled via sensor ID 511 permitting electronic sub-system 520 to determine the location of the optical sensor 300 and, if desired, the specific sample which the individual optical sensor 300 is designed to detect. In an embodiment of the present invention, a plurality of optical sensors 300 can be placed in a remote field or facility, or combination thereof and the location and sample type determined via sensor ID 511. By including sensor ID 511 on a plurality of optical sensors 300 on or in the optical sub-system 510, a distributive network of optical sensors 300 can be obtained. Accordingly, a plurality of sensor ID 511 types are possible, including a barcode, radio frequency tag, color code, a label, electronic signature or memory stored identifier.
In another embodiment shown in
The optical sensor 300 of the present invention can be used in conjunction with an OFC or OFM to increase the number of distinct types of chemical species to be analyzed and the sensitivity and dynamic range of the analysis system.
A sampling interface 514 of the optical sub-system 510 depends primarily upon the type of OFC 600 or OFM 610, 620, 630 used in the optical sub-system 510. Thus, direct contact, parallel flow, and static configurations are suitable OFC or OFM types. For example, the optical sensor 300 of the optical sub-system 510 can be manually introduced into the sample to make contact along a surface or other region of the optical sensor 300. Other sampling interfaces include fluidics, wherein the liquid sample is allowed to run over the optical sensor 300. In one use of the invention, the optical sub-system 510 is used in-situ and the electronic sub-system 520 is held at distance from the optical sub-system 510.
On the electronic sub-system 520 side, various functional features are provided and operationally coupled to each other. A source of power 521 is provided to activate and run the various active components of the electronic sub-system 520. Power source 521 can be solar, battery driven, alternating current, direct current, a generator or a remote power source, according to the invention.
An interface 522 gives the user input and functional control of the electronic sub-system 520 depending on the specific application of the analysis system 500. A keyboard, control pad, mouse, touch screen or other forms of control and input may form part of the interface 522. Likewise, the interface 522 may be implemented as a remote control subassembly of the electronic sub-system 520 which is operationally coupled to the analysis system 500 for remote use and operation. In yet another contemplated embodiment, the interface 522 comprises a switch or button which the user activates in order to command sensor functions.
Software/firmware 523 may be maintained on the electronic sub-system 520 to control the various sensors functions and processes according to the specific sensor application. In one embodiment, the software/firmware 523 is controlled by the user interface 522 allowing the user to view and display data results via display 525 and/or otherwise manipulate the sample related data as obtained by the optical sub-system 510.
For example, the user can use interface 522, software/firmware 523, and display 525 to determine when the sample of interest is detected by the optical sub-system 510. The data can be manipulated, graphed or otherwise analyzed depending on software/firmware 523 features. A help system may also be included in the software/firmware 523 to assist the user with various analysis system 500 features. The software/firmware 523 may be used to store, retrieve or transmit data and/or commands to the sensor or a remote processing system according to the invention.
Also shown is a storage area 524 that can be a hard disk, floppy disk or other magnetic means of storage or a chip-based storage device such as DRAM, EEPROM, flash memory, ROM or other similar components. Storage area 524 provides a space where sample related data, test history, calibration information or other similar data can be stored.
A display 525 may be included and operationally coupled to the various components of the electronic sub-system 520. In an embodiment of the analysis system 500, display 525 comprises one or more LEDs which are actuated at times when the optical sub-system 510 detects the presence of the particular sample of interest. In other embodiments, display 525 comprises a liquid crystal display (LDC), a monitor or CRT which provides alpha-numeric output relating to the sample of interest. Other displays 525 include hard copy, digital or analog signal outputs, audio alarm, synthetic voice, pager or projection among others.
Also shown is an electronic circuit 526 that includes a signal processor 527 in the electronic sub-system side 520 of the analysis system 500 which converts, processes, assembles and otherwise manipulates the data received from the optical sub-system 510. In one embodiment, the optical sub-system 510 generates a digital bitstream data output related to the sample of interest which is relayed via communications interface 550 to the electronic sub-system 520 and received by the signal processor 527 for further analysis. The data may be the output of an analog-digital converter which may be integrally molded on the optical sensor 300 or mounted externally.
In another embodiment, the output from the optical sub-system 510 is a modulated carrier that is transmitted to the signal processor 527 of the electronic circuit 526 via a wireless communications mode of communications interface 550.
For example, an RF transmitter can be incorporated in the optical sub-system 510 as part of communications interface 550 and used to modulate an airborne signal which is received by the communications interface 550 side of the electronic sub-system 520 and transferred to the signal processor 527 for demodulation and further analysis.
IoR measurements are sensitive to the temperature of the liquid under analysis. Furthermore, temperature changes of the optical sensor housing will lead to changes in optical properties of the photo detector 110 and other optical components, which lead to “false” readings that adversely affect concentration measurements. In order for the present invention to be fully automated and highly accurate, temperatures of both the optical sensor housing and the fluid under analysis are closely monitored and temperature changes are compensated for.
Embodiments of the present invention utilize a three-stage method for calibration, measurement, and conversion of IoR to liquid chemical concentration. For example, in stage 1 of the method, the calibration method shown in
In stage 2, a temperature compensated IoR may be calculated utilizing a linear equation using a sensor temperature measured by the thermistor 125 in the optical sensor 300 and a known fluid temperature measured by a thermistor 148 placed on the backside of the optical window 147. See equation 2 below.
Most liquids have a linear relationship between temperature compensated Index of Refraction (IoRTC) and concentration; therefore, two points on a line are often enough for a conversion. Furthermore, these two points will be the same for all sensors, so that the table (or curve) for a given chemical only has to be generated once. Referring to
In stage 2, the signal processor 527 determines IoRTC using a sensor temperature measured by the thermistor 125 in the optical sensor 300, a known fluid temperature measured by the thermistor(s) 148, the measured Index of Refraction as a function of time, and the following equation (see
IoR TC =IoR−A(T f−20)+B(T s−20);
Where IoRTC is the temperature compensated Index of Refraction, IoR is the measured Index of Refraction, Tf is the known temperature of the fluid, Ts is the temperature of the sensor, and A and B are constants.
In an alternative embodiment of the present invention, equation (3) is used in a firmware algorithm to perform temperature compensation of the concentration measurement as follows:
C compensated =C uncompensated +A(T 148 −T calibration)+B(T 125 −T 148) (3)
Where T148 is the temperature reading from thermister 148, T125 is the temperature reading from thermister 125, and A and B are constants determined from initialization and calibration. Note that equation (3) is a generalization of equation (2) above. Furthermore, equation (3) is written alternatively in terms of “chemical concentration,” where as equation (2) is written in terms of IoR.
A key innovation of the present invention is that by eliminating sensor-to-sensor variations in IoR, the three-stage calibration method becomes sensor independent. The signal processor 527 may display the calculated concentration using, for example, display 525, a graphical user interface (GUI) or an LCD display.
Next, the signal processor 527 calibrates 13102 the Index of Refraction to pixel position using known concentrations of the known sample under test, chemical X. A polynomial least squares fit to a plurality of calibration points is used to generate the calibration curve of known chemical X (see
In one embodiment of the present invention, step 13205 is utilized to normalize the TIR data set. The signal processor 527 normalizes the reflectivity data set by dividing the reflectivity data set by the average value of the intensity of a set of pixels located in the middle portion of the peak area of the reflectivity data set (see
Alternatively, according to a second embodiment, step 13206 may be utilized to normalize the TIR data set. This involves an automated adjustment of LED light source brilliance.
Embodiments of the present invention automatically correct and compensate for LED brightness changes. Referring to
The TIR data is numerically differentiated via a “smooth derivative” procedure:
Where the range of k and the number 60 determine the degree of smoothness.
The algorithm used is a weighted Mass Moment (MM) calculation. The weighted MM is shown in the equations below:
Yi=Ln [1+exp(100×(S i −T h))]−Ln [1+exp(100×(0−T h))] (8)
The weighted MM calculation gives more weight or emphasis to pixels near the mass moment pixel position of the first derivative. The values a and b are pixel numbers determined by empirical means that include the minimum of the numerical first derivative (see
The MM value is shown in
An analysis system 500 has been defined that incorporates miniaturized sensor technology having fixed optics inside a rigid, self-contained sensor platform or housing. The analysis system 500 combines an assortment of communications interface 550 which permits the integrated miniaturized optical sensor 300 of optical sub-system 510 to be placed at or near the sample of interest without interference from field personnel.
While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
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|U.S. Classification||356/136, 356/436, 356/445|
|International Classification||G01N21/55, G01N21/41|
|Cooperative Classification||G01N21/552, G01N21/0303, G01N21/4133|
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